Correctly show rebase state in MR widget

Correctly shows the rebase state even if a merge requests pipeline
has failed.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/45942

app/assets/javascripts/vue_merge_request_widget/stores/get_state_key.js

@@ -13,6 +13,8 @@ export default function deviseState(data) {
     return stateKey.conflicts;
   } else if (data.work_in_progress) {
     return stateKey.workInProgress;
+  } else if (this.shouldBeRebased) {
+    return stateKey.rebase;
   } else if (this.onlyAllowMergeIfPipelineSucceeds && this.isPipelineFailed) {
     return stateKey.pipelineFailed;
   } else if (this.hasMergeableDiscussionsState) {
@@ -25,8 +27,6 @@ export default function deviseState(data) {
     return this.mergeError ? stateKey.autoMergeFailed : stateKey.mergeWhenPipelineSucceeds;
   } else if (!this.canMerge) {
     return stateKey.notAllowedToMerge;
-  } else if (this.shouldBeRebased) {
-    return stateKey.rebase;
   } else if (this.canBeMerged) {
     return stateKey.readyToMerge;
   }

changelogs/unreleased/mr-rebase-failing-tests.yml

+---
+title: Fixed rebase button not showing in merge request widget
+merge_request:
+author:
+type: fixed

spec/javascripts/vue_mr_widget/stores/get_state_key_spec.js

@@ -76,4 +76,28 @@ describe('getStateKey', () => {
 
     expect(bound()).toEqual('archived');
   });
+
+  it('returns rebased state key', () => {
+    const context = {
+      mergeStatus: 'checked',
+      mergeWhenPipelineSucceeds: false,
+      canMerge: true,
+      onlyAllowMergeIfPipelineSucceeds: true,
+      isPipelineFailed: true,
+      hasMergeableDiscussionsState: false,
+      isPipelineBlocked: false,
+      canBeMerged: false,
+      shouldBeRebased: true,
+    };
+    const data = {
+      project_archived: false,
+      branch_missing: false,
+      commits_count: 2,
+      has_conflicts: false,
+      work_in_progress: false,
+    };
+    const bound = getStateKey.bind(context, data);
+
+    expect(bound()).toEqual('rebase');
+  });
 });